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3 CHAPTER 1 INTRODUCTION Fifty-seven percent of the 37,795 fatal crashes in the United four-lane divided expressways, and four-lane freeways road- States during 2001 occurred on two-lane undivided high- ways from six U.S. states (Illinois, Missouri, Pennsylvania, ways, compared with just 6.1 percent of fatal crashes that New York, Wisconsin, and New Jersey) were collected, aim- occurred on four-lane divided highways (1). Over one-third ing to undertake a statistically defendable analysis of their of the fatal crashes on two-lane undivided highways and crash experience. 27 percent of the fatal crashes on four-lane divided highways The six states were selected after undertaking a detailed occurred during dark or unlighted conditions. The majority survey of PRPM implementation practices and an assessment of those crashes involved only one vehicle. Any safety mea- of data availability (to support a safety evaluation of PRPMs) sure that has the potential to increase visibility and assist in 29 U.S. states with known PRPM installations. drivers in staying within their lanes should therefore be given A review of literature pertaining to past research on the serious consideration. safety effect of PRPMs and a survey of current PRPM imple- Pavement markings and other delineation devices provide mentation practices were undertaken during the first quarter drivers with information about their position within their own of 2002. The literature review identified critical design param- lane and information about which lanes are available for their eters, data requirements, methodological issues, and chal- use, especially at night. In addition, delineation devices pro- lenges. These were carefully studied before the formulation vide the driver with a preview of upcoming changes in the and implementation of the study design. roadway geometry, including curves, lane drops, narrowing, A literature review of the human factor issues pertaining the start and end of passing zones, crosswalks, and intersec- to PRPMs was executed. The knowledge from these past tions. Permanent raised pavement markers (PRPMs) are research studies was used in the interpretation of the safety delineation devices that are often used for centerline, lane evaluation results and the development of PRPM implemen- divider line, and, more rarely, edgeline applications to tation guidelines. improve preview distances and guidance for drivers in Two types of safety data analyses were performed: (1) a inclement weather and low-light conditions. composite analysis that determined the overall effect of Recent studies in New York, Texas, and Pennsylvania, PRPMs, by state, for a number of different crash types (e.g., which are discussed in Chapter 2, have raised concerns about nighttime, wet weather, and guidance) and (2) a disaggregate the safety effects of PRPMs after potential negative side analysis that investigated the relationships between the safety effects were reported. These studies are among the few that effect of PRPMs on nighttime crashes and a number of critical have been performed to date to determine the effect of PRPMs roadway, traffic, and PRPM design parameters. The results on highway safety. These studies pertained to single juris- of these analyses were used to develop, in combination with dictions only, and their results were questionable because of human factors considerations, a comprehensive set of guide- some data and methodological difficulties. NCHRP Project lines for the application of PRPMs, as well as an engineering 5-17 responded to the need to use state-of-the-art analytical procedure for estimating the anticipated cost-effectiveness of methods and comprehensive data to assess the safety effects PRPMs at a particular location. of PRPMs and to identify critical design parameters. The pri- The body of this report has been structured into six addi- mary objectives of NCHRP Project 5-17, as presented in the tional chapters: the findings from the review of the PRPM- project statement, were "to assess the safety effects of per- related literature and jurisdictional practices (Chapter 2), data manent raised pavement markers (PRPMs) and to develop collection and preparation (Chapter 3), safety impact analy- guidelines for their use." sis of PRPM installations (Chapter 4), a discussion of study To achieve these objectives, data related to snowplowable results (Chapter 5), guidelines for the use of snowplowable PRPM, nonintersection locations along two-lane roadways, PRPMs (Chapter 6), and study conclusions (Chapter 7).